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  Section: Plant Protocol » Environmental Science Methodology
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Determination of Solids in Water


The aim of the experiments is to determine the following types of solids in the given sample(s):
(a) Total solids
(b) Total (inorganic) fixed solids
(c) Total volatile (organic) solids
(d) Total dissolved solids
(e) Dissolved fixed (inorganic) solids
(f) Dissolved volatile (organic) solids
(g) Total suspended solids
(h) Suspended fixed (inorganic) solids
(i) Suspended volatile (organic) solids
(j) Settleable solids

‘Total solids’ is the term applied to the material left in the vessel after evaporation of a sample of water/waste water and its subsequent drying in an oven at a definite temperature. Total solids include “total suspended solids” the portion of total solids retained by a filter and “total dissolved solids” the portion that passes through the filter. Fixed solids is the residue remaining after ignition for 1 hour at 550°C. The solid portion that is volatilised during ignition is called volatile solids. It will be mostly organic matter. Waters that are low in organic matter and total mineral content and are intended for human consumption may be examined under 103–105°C or 179–181°C. But water containing considerable organic matter or those with pH over 9.0 should be dried at 179–181°C. In any case, the report should indicate the drying temperature.

The sample is filtered and the filtrate evaporate in a weighed dish on a steam bath, the residue left after evaporation is dried to constant weight in an oven at either 103–105°C or 179–181°C. The increase in weight over that of the empty dish represents total dissolved solids and includes all materials, liquid or solid, in solution or otherwise, which passes through the filter and not volatilised during the drying process.

The difference between the total solids and the total dissolved solids will give the total suspended solids. The dishes with the residue retained after completion of the tests for total solids and total dissolved solids are subjected to heat for 1 hour in a muffle furnace held at 550C. The increase in weight over that of the ignited empty vessel represents fixed solids in each instance.

The difference between the total dissolved/total suspended solids and the corresponding fixed solids will give volatile solids in each instance. All the quantities should be expressed in mg/L. Settleable matter in surface and saline waters as well as domestic and industrial wastes may be determined and reported on a volume basis as millilitre per litre.

1. Porcelain evaporating dishes of 150-200 mL capacity
2. Steam bath
3. Drying oven
4. Desiccators
5. Analytical balance or monopan balance
6. Filter paper (preferably of glass fibre)
7. Electric muffle furnace
8. Imhoff cone


(a) Total solids
  1. Ignite the clean evaporating dishes in the muffle furnace for 30 minutes at 550C and cool in a desiccator.
  2. Note down the empty weight of the dish (W1).
  3. Pour a measured portion (50 to 100 mL) of the well-mixed sample into the dish and evaporate the contents by placing the dish on a steam bath.
  4. Transfer the dish to an oven maintained at either 103-105C or 179-181C and dry it for 1 hour.
  5. Allow the dish to cool briefly in air before placing it, while still warm in a desiccator to complete cooling in a dry atmosphere.
  6. Weigh the dish as soon as it has completely cooled (W2).
  7. Weight of residue = (W2 - W1) mg.
    W2 and W1 should be expressed in mg.
(b) Total fixed solids
  1. Keep the same dish used for determining total residue in a muffle furnace for 1 hour at 550C.
  2. Allow the dish to partially cool in air until most of the heat has dissipated, then transfer to a desiccator for final cooling in a dry atmosphere.
  3. Weigh the dish as soon as it has cooled (W3).
  4. Weight of total fixed residue = (W3 - W1) mg.
    W3 and W1 should be expressed in mg.
(c) Total dissolved solids
  1. Filter a measured portion of the mixed sample (50 or 100 mL) through a filter paper and collect the filtrate in a previously prepared and weighed evaporating dish.
  2. Repeat the steps 3 to 6 outlined in total solids procedure.
  3. Weight of dissolved solids = (W5 - W4) mg.
    W4 = Weight of empty evaporating dish in mg.
    W5 = Weight of empty evaporating dish in mg + Residue left after evaporating the filtrate in mg.
(d) Total suspended solids = Total solids - Total dissolved solids.

(e) Total volatile solids = Total solids - Total fixed solids.

(f) Fixed dissolved solids
  1. Keep the same evaporating dish used in determining total dissolved solids in a muffle furnace for 1 hour at 550C.
  2. Repeat the steps 2 and 3 outlined in total fixed solids procedure.
  3. Weight of fixed dissolved solids = (W6 - W4) mg.
    W6 = Weight of empty evaporating dish + Fixed solids left after ignition at 550C.
(g) Volatile dissolved solids = Total dissolved solids - Fixed dissolved solids.

(h) Fixed suspended solids = Total fixed solids - Fixed dissolved solids.

(i) Volatile suspended solids = Total volatile solids - Volatile dissolved solids.

(j) Settleable solids by volume
  1. Fill an imhoff cone to the litre mark with a thoroughly mixed sample.
  2. Settle for 45 minutes.
  3. Gently stir the sides of the cone with a rod or by spinning.
  4. Settle 15 minutes longer.
  5. Record the volume of settleable matter in the cone as mL/L.

1. mg/L total solids = mg total solids 1000
mL of sample

2. mg/L total fixed solids = mg total fixed solids 1000
mL of sample

3. mg/L total dissolved solids = mg of total dissolved solids 1000
mL of sample

4. mg/L total suspended solids = mg/L of total solids - mg/L of total dissolved solids

5. mg/L total volatile solids = mg/L of total solids - mg/L of total fixed solids

6. mg/L fixed dissolved solids = mg fixed dissolved solids 1000
mL of sample

7. mg/L volatile dissolved solids = mg/L total dissolved solids - mg/L of fixed dissolved solids

8. mg/L fixed suspended solids = mg/L total fixed solids - mg/L fixed dissolved solids

9. mg/L volatile suspended solids= mg/L total volatile solids - mg/L volatile dissolved solids



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